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Lee S.-H.,Kyungpook National University | Lee S.-H.,CRESIN Co. | Choi S.-H.,Hannam University | Gopalan S.-A.,Kyungpook National University | And 2 more authors.
International Journal of Hydrogen Energy | Year: 2014

In this work, a combination of constituent materials capable of improving the moisture retention and proton conductivity (PC) was incorporated into sulfonated poly (ether ether ketone) (SPEEK) membranes in order to prepare new, self-humidifying composite membranes (SHMs) for proton exchange membrane fuel cells. The property-improving components were incorporated into the cast SPEEK film in an appropriate microstructural architecture to prepare the SHMs with increased water retention and PC. SHMs were therefore prepared with the inclusion of carboxyl-functionalized graphene (G(c)) and phosphotungstic acid (PWA) with varying proportions into the SPEEK film. The structure of the SPEEK/G(c)/PWA composite membranes was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy. The physicochemical properties of the composite membranes, such as ion exchange capacity, water uptake, thermal stability and PC, were investigated. This work provides confirmation that self-humidifying properties are improved at temperature above 60 °C through a combinational inclusion of G(c) and PWA within SPEEK and the new self-humidifying membranes have potential for use in medium temperature direct methanol fuel cells. © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Kim S.Y.,Seoul National University | Kim J.Y.,LG Chemical Ltd | Kim S.H.,Seoul National University | Lee S.H.,Seoul National University | And 3 more authors.
Korea Australia Rheology Journal | Year: 2010

Non-uniform temperature distribution is developed in the thickness direction of the film insert molded (FIM) product during filling and cooling stages due to retardation of the heat transfer through the solid film. Since the non-uniform temperature distribution causes non-uniform shrinkage of the product after ejection and warpage is generated by the non-uniform shrinkage, warpage of the FIM specimen is larger than that of the injection molded specimen. A new mold design was suggested in this study in order to prevent warpage of FIM specimens. Warpage of FIM specimens obtained by using the new mold was smaller than that of FIM specimens obtained by using the conventional mold. Fiber reinforced polymer resins were also used as the substrate to prepare the FIM specimens. Warpage of the FIM specimens with the fiber composite substrate was reduced with increasing the fiber loadings. Warpage of the FIM specimens with carbon fiber (CF) reinforced PC (polycarbonate)/ABS (acrylonitrile-butadiene-styrene) blend was predicted by considering anisotropic material properties such as fiber orientation, thermal expansion coefficient, Poisson's ratio, and elastic modulus. © 2010 by The Korean Society of Rheology.


Baek S.J.,Cresin Co. | Kim S.Y.,Cresin Co. | Youn J.R.,Cresin Co. | Kim K.W.,Seoul National University
Fibers and Polymers | Year: 2011

Mechanical properties of chopped carbon fiber (CF) reinforced PC/ABS composites were investigated. Tensile strength and elastic modulus of the composites were enhanced with increasing CF contents. On the contrary, impact strength of the composite was decreased with increasing CF fraction. Film insert molding was introduced in order to improve impact strength. Film insert molded composite specimens have higher impact strength than conventional injection molded composite specimens because inserted film acted as a cushion to absorb the impact energy. Large warpage which was observed after molding and known as a disadvantage of the film insert molded part can be prevented by controlling the amount of filled CFs. Therefore, fiber reinforcement and film insert molding can be applied simultaneously to reduce warpage of the film insert molded part and enhance impact strength of the CF reinforced composite. © 2011 The Korean Fiber Society and Springer Netherlands.


Kim S.Y.,Seoul National University | Shin K.S.,Seoul National University | Shin K.S.,Dongwoo Finechem Co. | Lee S.H.,Seoul National University | And 3 more authors.
Fibers and Polymers | Year: 2010

Although poly(lactic acid) (PLA) possesses many desirable properties such as miscible, reproducible, nontoxic, and biodegradable properties, extremely slow crystallization rate is a weak point in comparison with other commercial thermoplastics. Addition of nucleating agents can be a good method to increase the overall crystallization rate and multi-walled carbon nanotube (MWCNT) is generally known as a good nucleating agent as well as reinforcement. MWCNT reinforced PLA nanocomposites were prepared by melt blending and the unique nucleation and crystallization behaviors of pure PLA and MWCNT/PLA nanocomposites were investigated. Slow homogeneous nucleation and crystallization behavior of the pure PLA and fast heterogeneous crystallization behavior of MWCNT/PLA nanocomposites were observed. Crystallization behavior of MWCNT/PLA nanocomposites was irrespective of cooling rate and the peculiar behavior was due to fast heterogeneous crystallization caused by the nucleating effect of MWCNT and fast PLA chain mobility. © 2010 The Korean Fiber Society and Springer Netherlands.


Lim S.K.,Daegu Gyeongbuk Institute of Science and Technology | Choi W.M.,Daegu Gyeongbuk Institute of Science and Technology | Choi H.J.,Daegu Gyeongbuk Institute of Science and Technology | Hong S.H.,Daegu Gyeongbuk Institute of Science and Technology | And 4 more authors.
Advanced Materials Research | Year: 2013

Poly (ethylene terephthalate)(PET)/ Al2O3 nanocomposites via in situ polymerization were studied. The nanoparticle loading was varied from 0.3 to 1 wt.%. From the DSC results, no significant differences were recorded for melting temperatures. However, simple added PET/ Al2O3nanocomposites slightly changed to the lower melting temperature. Morphology of the nanocomposites has been examined by SEM. From the SEM results revealed that dispersed Al2O3 nanoparticles in the EG (ethylene glycol) during the polymerization can be well dispersed in PET matrix. © (2013) Trans Tech Publications, Switzerland.

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